An examination by The New York Times of 100 rampage murders found that most of the killers spiraled down a long slow slide, mentally and emotionally. Most of them left a road map of red flags, spending months plotting their attacks and accumulating weapons, talking openly of their plans for bloodshed. Many showed signs of serious mental health problems.

But in case after case, the Times review found, the warning signs were missed: by a tattered mental health care system; by families unable to face the evidence of serious mental turmoil in their children or siblings; by employers, teachers and principals who failed to take the threats seriously; by the police who, when alerted to the danger by frightened relatives, neighbors or friends, were incapable of intervening before the violence erupted.

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In 34 of the 100 cases, however, families or friends of the killers desperately did try to find help for a person they feared was a ticking time bomb, but were rebuffed by the police, school administrators or mental health workers.

Sylvia Seegrist caromed in and out of mental institutions 12 times in 10 years, while her parents searched for a residential program where she could stay in treatment. They knew she was dangerous. She had stabbed a psychologist and tried to strangle her mother, and had hidden a gun in her apartment. But each time, she was released from the hospital when she seemed to improve.

"We were always fearful that maybe some tragedy would happen," said Ruth S. Seegrist, Sylvia's mother. "She threatened it: 'Someday before I kill myself, I'll bring some people down with me.' " Sylvia opened fire in a suburban Philadelphia shopping mall in 1985, killing three people and wounding seven.

[T]he Holmes case raises a crucial question: Is there a way to identify and stop mass killers before they unleash themselves?

.... After Columbine, the Secret Service and the FBI undertook months-long projects that were designed to create methods to spot mass killers before they act. The Secret Service study, the more influential one, looked at 41 attackers in 37 school massacres. The data showed that mass shooters don't usually act impulsively and rarely make threats against enemies. But they do tend to have experience with firearms.

In short, mass murderers are a vexing and diverse lot. For instance, the typical mass killer said nothing suspicious to friends or family members but signaled his intent to third parties--especially, in the cases of the kids who shot up their schools, classmates they liked. On July 25, a report emerged, citing a law-enforcement source, that Holmes had taken the time to send a troubling package to a psychiatrist at the University of Colorado at Denver, where Holmes worked. He apparently sent drawings of his intended massacre.

In 2004 the journal Behavioral Sciences & the Law published an authoritative paper by a team of psychologists led by Reid Meloy, a professor at the University of California, San Diego. For the past decade, Meloy has been a consultant for the FBI's counterintelligence division.

In the paper, Meloy and his colleagues offered both sociological traits and behavioral clues that are associated with mass violence. Some of the factors they identified: A criminal history. The No. 1 predictor of violent crime is previous violent behavior. (For his part, Holmes had only a speeding ticket.)

A sense of victimization.

Most adolescents who shoot up their schools say they were bullied. Most adult mass murderers say girlfriends or relatives had recently rejected them or that they had been persecuted at work.

An age in the 20s.

According to the Meloy paper, the average age of mass killers is 27. (Holmes is 24.)

Other factors come up as well--for instance, preoccupation with fantasy is a common feature of mass killers, and Holmes is reported to have played video games ad libitum. But none of these facets can distinguish a burnout from a psychopath....